U.S. patent number 6,436,004 [Application Number 09/630,935] was granted by the patent office on 2002-08-20 for pulley slip control for continuous variable transmissions.
This patent grant is currently assigned to ZF Friedrichshafen AG. Invention is credited to Joachim Cichy, Hans-Dieter Hengstler, Bernd Loffler.
United States Patent |
6,436,004 |
Loffler , et al. |
August 20, 2002 |
Pulley slip control for continuous variable transmissions
Abstract
Within the scope of the process for variator slip treatment in
continuously variable automatic transmissions of a motor vehicle,
upon detection of variator slip, a characteristic field (1) of slip
meter is locally incremented according to ratio value (iv) and to
engine torque (M_mot) and simultaneously an evaluated slip meter
(2) of an evaluation module (3), likewise according to ratio value
(iv) and to engine torque (M_mot), is increased, wherein via the
evaluation module (3), the variator slip is assessed according to
duration and intensity. Besides, a characteristic field (4) of slip
status meter connected with the evaluated slip meter (2) is
incremented together with the evaluated slip meter (2), a signal
being passed on to an error memory (5) so that, with the entry of
the error, slip, evaluated slip and slip status meter are entered
in the error memory (5) as environmental conditions. Thereafter the
contact pressure security is locally varied according to the
characteristic field (4) of the slip status meter.
Inventors: |
Loffler; Bernd (Ravensburg,
DE), Hengstler; Hans-Dieter (Ravensburg,
DE), Cichy; Joachim (Kressbronn, DE) |
Assignee: |
ZF Friedrichshafen AG
(Friedrichshafen, DE)
|
Family
ID: |
7917676 |
Appl.
No.: |
09/630,935 |
Filed: |
August 2, 2000 |
Foreign Application Priority Data
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Aug 7, 1999 [DE] |
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199 37 472 |
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Current U.S.
Class: |
477/45 |
Current CPC
Class: |
F16H
61/66272 (20130101); F16H 61/12 (20130101); Y10T
477/624 (20150115) |
Current International
Class: |
F16H
61/66 (20060101); F16H 61/662 (20060101); F16H
61/12 (20060101); B60K 041/12 () |
Field of
Search: |
;477/44,45,46 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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44 11 628 |
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Oct 1995 |
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DE |
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195 05 561 |
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Aug 1996 |
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DE |
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404064760 |
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Feb 1992 |
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JP |
|
Primary Examiner: Marmor; Charles A.
Assistant Examiner: Pang; Roger
Attorney, Agent or Firm: Davis & Bujold, P.L.L.C.
Parent Case Text
The invention concerns a process for variator slip control in
continuously variable automatic transmissions.
Claims
What is claimed is:
1. A process for treatment of variator slip in a continuously
variable automatic transmission, the process comprising the steps
of, upon detection of variator slip, increasing a characteristic
field (1) of a slip meter according to a ratio value (iv) of a
variator and to an engine torque (M_mot) of a prime mover and
simultaneously an evaluated slip meter (2) of an evaluation module
(3), likewise according to the ratio value (iv) of the variator and
to the engine torque (M_mot), is increased, assessing the variator
slip according to a duration and an intensity by the evaluation
module (3), and increasing a characteristic field (4) of a slip
status meter connected with said evaluated slip meter (2) together
with said evaluated slip meter (2), passing a signal to an error
memory (5) in such a manner that, with the entry of an error, the
slip, an evaluated slip and a slip-status meter are entered in said
error memory (5) as environmental conditions and, depending on the
characteristic field (4) of the slip-status meter, a contact
pressure security of said variator is locally varied as a function
of the variator ratio (iv) and the engine torque (M_mot), and
deleting the error entry by deletion of the error memory (5), and
said characteristic field (4) of said slip status meter being
deleted independently and separately of said error memory.
2. The process according to claim 1, further comprising the step of
locally decreasing the characteristic field (4) of the slip-status
meter once a desired behavior of the transmission is achieved.
3. The process according to claim 1, further comprising the step of
testing whether a whole contact pressure security of the variator
exceeds a specific level and, if the contact pressure security of
the variator exceeds the specific level, entering a second error
information in said error memory (5) and allowing a system to react
with a substitute function in order to protect the system.
Description
BACKGROUND OF THE INVENTION
A continuously variable automatic transmission (CVT) usually
consists, among others, of a starting unit, a forward/reverse drive
unit, an intermediate shaft, a differential, hydraulic and
electronic control devices and one variator. A customary variator
construction is a belt-drive variator, having a primary and a
secondary pulley, wherein both pulleys are formed by beveled
pulleys disposed in pairs and, wherein the variator is provided
with a torque transmitting belt-drive variator, having a primary
and a secondary pulley, wherein both pulleys are formed by beveled
pulleys disposed in pairs and, wherein the variator is provided
with a torque transmitting belt-drive element which rotates between
the two beveled pulley pairs. In such a transmission, the actual
ratio is defined by the running radius of the belt-drive element
which, in turn, is function of the axial position of the beveled
pulleys. A CVT is consequently a positive-engagement transmission;
the engine torque is transmitted by (static) friction between the
belt-drive element and the variator pulleys.
In the prior art, the variator is mostly functionally divided in
one side for control of the change of ratio (adjustment) and, in
other side, for adjustment of the necessary contact pressures
(tightening) which ensure the required contact between the pulley
and the belt-drive element so that no slip generates. Depending on
the operating point, either the primary or the secondary pulley is
used for setting the contact pressures.
For this purpose, the transmission control adjusts on the variator
a hydraulic contact pressure in order to make the momentary
transmission of the engine torque possible. The main input
variables for the pressure are the momentary transmission input
torque and the transmission ratio. The contact pressure must be as
high as needed and as low as possible; if the pressure is too low,
the slipping of the variator (slip) results and therewith a damage
to the transmission. If the pressure is too high, the efficiency of
the transmission is unnecessarily impaired.
The contact pressure requirement is affected by many parameters not
predictable at the time such as oil aging, smoothing of the pulley
surface or kind of oil.
To prevent slippage between the pulley and the belt-drive element,
the teaching of the prior art is to impose increased security or
security factors on the calculated control pressure values. This
procedure has the disadvantage that thereby the efficiency of the
automatic transmission is impaired. Therefore, the increased
security (security factor) must be selected as small as
possible.
SUMMARY OF THE INVENTION
Accordingly, the problem on which this invention is based is to
outline, departing from the cited prior art, a process for variator
slip treatment and for protection of the variator for a CVT so as
to obtain the best possible efficiency of the transmission and, at
the same time, improve the prevention of damages to the
transmission.
The inventive process must adapt the contact pressure to the
operating point position so that it becomes possible to reduce the
effects of an overpressure to a minimum which affects the
efficiency.
According to the invention, this problem is solved with the
features of claim 1. Other embodiments of the invention result form
the sub-claims.
Accordingly, when the variator slip is detected, it is proposed
locally to increment in the place where the slip occurs a slip
meter characteristic field depending on the ratio value iv of the
variator and on the engine torque M_mot f (iv, M_mot) and at the
same time increase, via an evaluation module, an evaluated slip
meter, the variator slip being assessed by means of the evaluation
module according to duration and intensity.
It is further proposed to add to the evaluated meter a
characteristic field of slip-status meter which is incremented with
the evaluated slip meter.
Parallel to incrementing the meters, a belt slip error is entered
in a diagnosis or error memory so that with the entry of the error,
slip, evaluated slip and slip-status meter are entered as
environmental conditions in the diagnosis or error memory.
According to the invention, unlike the belt-slip meter, the status
meter can be locally decremented via a "self-healing function" when
the transmission behavior is perfect with regard to the variator
slip.
The status meter serves as factor for locally lifting the contact
pressure security f(iv, M_mot) whereby in case of unnecessary slip
detection or self-healing processes in the transmission mechanics
(e.g. smoothing of the pulleys in the belt-drive variator), the
contact pressure security can be again withdrawn which results in
improvement of the efficiency.
The whole contact pressure security also results from other
security factors to be taken into account. If the total contact
pressure security exceeds a specific level (e.g. system limit or
breaking limit), then a second error information is entered in the
diagnosis memory (error memory), which information can be reacted
to with other substitute function (e.g. hydraulic emergency
running).
By deletion of the diagnosis or error memory, the error entries can
be deleted but not belt slip meter and status meter. These are
independent of the error memory and can be separately deleted. A
resetting of the whole function by deleting the transmission
diagnosis is thereby eliminated.
The switch for resetting slip and slip status meter must be
provided with greater securities (qualifications) than the deletion
of the diagnosis memory.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is explained, in detail herebelow, with reference to
the enclosed FIGURE which shows a block circuit diagram
illustration of the inventive process. In the embodiment shown, the
variator is designed as belt-drive variator, wherefore the variator
slip examined is a belt slip.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As is to be understood from the FIGURE, upon detection of belt
slip, a characteristic field 1 of belt slip meter is locally
incremented in accordance with the ratio value iv and with the
engine torque M_mot and simultaneously an evaluated belt slip meter
2 of an evaluation module 3 is increased likewise in accordance
with the ratio value iv and with the engine torque M_mot, the belt
slip being assessed by means of the evaluation module 3 according
to duration and intensity. With the evaluated belt slip meter 2 is
connected a characteristic field 4 of belt slip status meter so as
to be incremented together with the evaluated belt slip meter
2.
According to the invention, upon detection of belt slip, a signal
is transmitted to a diagnosis or error memory 5 in order to
indicate a symptom error of belt slip; the entry takes place in a
manner such that, with the entry of the error, belt slip, evaluated
belt slip and belt slip status meter are entered in the diagnosis
memory as environmental conditions. This is made clear in the
FIGURE by the arrows A, B and C as logical module linkages.
According to the invention, depending on the characteristic field 4
of belt slip status memory, the contact pressure security, which is
function of variator ratio and engine torque M_mot, is locally
varied. Thereby, It is ensured that, in case of an unnecessary belt
slip detection or self-healing process in the transmission
mechanics (smoothing of the pulleys), the contact pressure security
is again withdrawn.
Within the scope of a preferred embodiment, the characteristic
field 4 of belt status meter is locally decremented when the
transmission behavior is perfect.
Thereafter is tested whether the whole contact pressure security
exceeds a specific level (e.g. system limit or breaking limit).
When this case occurs, a second error information is entered in the
error memory 5 to which it is reacted with one other substitute
function (e.g. hydraulic emergency running) in order to protect the
system.
* * * * *